Modeling young's modulus of polymer-layered silicate nanocomposites using a modified halpin - Tsai micromechanical model

In this study nanocomposites consisting of an epoxy matrix filled with silicate clay particles are investigated. Recent and ongoing research has shown that dramatic enhancements can be achieved in stiffness and thermal properties in these nanocomposites with small amounts of particle concentration. The resulting properties of nanocomposites are intimately related to the microstructure achieved in processing these materials. However, the ideal situation of full exfoliation, dispersion, and orientation is not usually achieved. A more common case is the partial exfoliation and intercalation. The latter is a process whereby the polymer penetrates the interlayer spaces of clay particles, causing an increase in the layer spacing (d-spacing). The region consisting of a matrix with exfoliated clay nanolayers or platelets is analyzed by assuming a near uniform-dispersion and a random orientation. The properties of intercalated clusters of clay platelets are calculated by a rule of mixtures based on a parallel platelet system. The modified composite theory of Halpin - Tsai is applied to calculate the modulus of the nanocomposite as a function of the clay concentration for various parametric variations, including the exfoliation ratio, the particle/matrix stiffness ratio Ef/Em, the particle volume fraction f, and the particle aspect ratio L/t. The modified composite theory satisfactorily captures the stiffness behavior of the polymer/clay composites.